Editing Frequency-hopping spread spectrum (section)

==Technical considerations==
The overall bandwidth required for frequency hopping is much wider than that required to transmit the same information using only one [[carrier frequency]]. But because transmission occurs only on a small portion of this bandwidth at any given time, the instantaneous interference bandwidth is really the same. While providing no extra protection against wideband [[thermal noise]], the frequency-hopping approach reduces the degradation caused by narrowband interference sources.

One of the challenges of frequency-hopping systems is to synchronize the transmitter and receiver. One approach is to have a guarantee that the transmitter will use all the channels in a fixed period of time. The receiver can then find the transmitter by picking a random channel and listening for valid data on that channel. The transmitter's data is identified by a special sequence of data that is unlikely to occur over the segment of data for this channel, and the segment can also have a [[checksum]] for integrity checking and further identification. The transmitter and receiver can use fixed tables of frequency-hopping patterns, so that once synchronized they can maintain communication by following the table.

In the US, [[Title 47 CFR Part 15|FCC part 15]] on unlicensed spread spectrum systems in the 902–928&nbsp;MHz and 2.4&nbsp;GHz bands permits more power than is allowed for non-spread-spectrum systems. Both FHSS and direct-sequence spread-spectrum (DSSS) systems can transmit at 1 watt, a thousandfold increase from the 1 milliwatt limit on non-spread-spectrum systems. The FCC also prescribes a minimum number of frequency channels and a maximum dwell time for each channel.